The unexpected discovery was made during experiments intended to find out exactly how long spiders can survive underwater—a number of spiders and insects have long been known to be resistant to drowning.

Scientists at the University of Rennes in France collected three species of wolf spider—two from salt marshes, one from a forest. The team immersed 120 females of each species in seawater, jostling the spiders with brushes every two hours to see if they responded.

As expected, all the forest wolf spiders (Pardosa lugubris) apparently died after 24 hours. The two salt marsh-dwelling species took longer—28 hours for Pardosa purbeckensis and 36 hours for Arctosa fulvolineata.

After the "drownings," the researchers, hoping to weigh the spiders later, left them out to dry. That's when things began to get weird.

Good as New

Hours later, the spiders began twitching and were soon back on their eight feet.

"This is the first time we know of arthropods returning to life from comas after submersion," said lead researcher Julien Pétillon, an arachnologist now at Ghent University in Belgium.

Marsh-dwelling A. fulvolineata, which took longest to "die," typically requires about two hours to recover, the researchers discovered.

In the wild, the species doesn't avoid water during flooding, while the other salt marsh species generally climbs onto vegetation to avoid advancing water.

The spiders' survival trick depends on a switch to metabolic processes—the processes that provide energy for vital functions in the body—that do not require air, the researchers speculate.